Method and apparatus for deoxidizing and degasifying liquid steel



METHOD AND APPARATUS FOR DEOXIDIZING AND DEGASIFYING LIQUID STEEL FiledSept. 18, 1939 lvwe 712 52" Marl l aQ/far y with the cast iron mould,chills rapidly and I the gases to the top of the ingot being formedPatented Aug. 19, 1941 METHOD AND APPARATUS FOR DEOXIDIZ- ING ANDDEGASIFYIN G LIQUID STEEL Baltzar E. L. de Mare, Philadelphia, Pa.

Application September 18, 1939, Serial No. 295,491 In Sweden September20, 1938 3 Claims.

This invention relates to the treatment of liquid steel, to improve thequality thereof by eliminating the two chief causes of defects inarticles formed therefrom, namely the elimination of products ofoxidation, chiefly silicates of manganese and aluminum which causenonmetallic impurities in the articles; and the elimination of occludedgases, such as hydrogen, nitrogen and carbon monoxide which cause seams.

The object of the invention is to provide a thoroughly practical methodfor such treatment, to replace methods hitherto known or proposed whichhave proven to be, in one or more respects, commercially impractical,ineillcient, or unadaptable and have therefore been discarded.

For instance, it has previously been proposed to pour molten metal intoa mould placedin an airevacuated chamber, to give the vacuum a chance toeliminate gases occluded in the metal. Thus, for instance, a wholeelectric furnace and one or more moulds have been placed under one largebell for evacuation. The bell therefore, was necessarily large in size,heavy, and unwieldy. Incidentally, the means for handling the furnaceand the mould, or moulds, were complicated and expensive.

It has also been proposed to arrange the moulds alone, with adistributing arrangement for the metal, in'a vacuum chamber, and toemploy a special ladle as a cover for the chamber, above thedistributing arrangement. This arrangement is necessarily diiiicult tohandle, bulky, and complicated and suffers further from the disadvantagethat the evacuation of the vacuum chamber cannot begin until the ladlehas been placed in position.

Normally the pouring of liquid metal directly into a mould under vacuuminvolves the disadvantage that the metal, upon making contact solidifiesbefore the vacuum can become effective to extract all the occluded gasesand before the slag and impurities can be carried upwards by in themould.

It has been proposed to provide a ladle or similar receptacle with atight cover connected with an evacuating arrangement, and on this coverto out breaking the connection with the evacuating arrangement.

Both of the last named arrangements have an additional disadvantage inthat the ladle in which the vacuum treatment is being carried out issurrounded by air, therefore the radiation of heat from the ladlebecomes considerable. For that reason the metal cannot'be permitted toremain for any prolonged period of time in the ladle. Therefore, thevacuum treatment cannot be continued for a sufficient length of time tobe thoroughly efiective.

It has also been proposed to treat the liquid metal with deoxidizingslag to remove oxides and other impurities from the metal, by causingthe metal to fall from a great height into a receptacle containing suchslag, to cause a violent impact therebetween for creating an intermixingof the two. This involves the'disadvantage that oxidization of the metaland loss of heat by radiation and convection increase in proportion tothe height of its fall.

The several disadvantages pointed out above in regard to the heretoforeknown methods and arrangements are avoided in the invention at hand,according to which the treatment can be carried out in a practical wayby the use of ordinary ladies and with the greatest possibleefiectiveness.

The present invention also ensures that the Pouring can be doneconveniently in the usual way and under atmospheric pressure, after thedeoxidizing and degasifying treatment has been finished.

The present invention is chiefly distinguished from the prior art inthat the liquid metal, tapped from a converter or melting furnace into aladle, is pouredfrom said ladle into a smaller open vessel or pouringbox arranged the shortest possible distance below the ladle and havingcontrolled communication with a vacuum chamber; in that the metal, whilein this vessel is subjected to electric heating and cleaning by asuitable deoxidizing slag; in that the liquid metal is permitted to flowfrom this vessel in a stream place a receptacle from which liquid metalcon-' top; and that the cover cannot be removed withdown into a ladleremovablyv enclosed in the vacuum chamber; inthat during its pouringinto the enclosed ladle the liquid metal is exposed to the action of ahigh vacuum; in that after' the pouring is completed the exposure'of theliquid metal to said high vacuum is continued for adesired period oftime; and in that the last named ladle,after the vacuum treatment hasbeen finished and atmospheric pressure restored, is taken out of thevacuum chamber and its content poured oil into moulds. Furtherdistinctive features and advantages of the invention will be madeevident by the following description and appended claims.

In the accompanying drawing is shown a design or an arrangement forcarrying out the method according to the invention, the single figure ofthe drawing being a vertical section of the preierred arrangement forthe vacuum treatment of liquid steel.

In the drawing, I denotes a vacuum chamber formed within a suitablestructure placed in the ground, such as a concrete pit 2, which may bereinforced with an outer air-tight casing 3, and provided with arefractory lining, as shown at l.

The vacuum chamber I is covered with a convex lid Ii, which is providedwith a suitable heatinsulating lining, for instance concrete, and withlifting clevlses 6 for the handling thereof. The lid 5, at its underedge, is provided with a laby rinth packing I, which consists of anumber of concentric ridges with sharp edges, which edges rest on amachine "finish bottom of a troughshaped channel 8 covered with asuitable plastic material into which said edges are pressed. The slopinginside wall 9 of the trough 8 forms a irusto-conical guide for the lid5.

n the lid 5, a small open vessel or pouring box Ill is mounted andsuitably secured. The vessel I0 communicates with the vacuum chamber Ithrough a nozzle I I disposed in the bottom of the vessel II). Theopening or hole of the nozzle II can be closed .or' opened by means of astopper rod II. The entrance of air into the vacuum chamber I is atfirst prevented by the stopper I2 and alter the level of the metal inthe vessel III is raised to a predetermined height the liquid metal inthe vessel III forms the necessary seal.

In the construction shown, the vessel I0 is surrounded by an electriccoil I3 and is designed as a high frequency electric furnace of theNorthrup type, for example. A

The lid of the vacuum chamber I can be provided with an air-admissionvalve 25 and a sight glass III for observation and for use of an opticalpyrometer for determining the temperature of the stream 28 in comparisonto the temperature 0! the stream 24, also determined by optical py"rometer, or with other arrangements, by which the course oi treatment inthe vacuum chamber I can be regulated or controlled, and according towhich the strength of the electric current in coil It can be suitablyregulated.

A ladle I8 is shown above the vessel III, by

which ladle the liquid steel is carried from the converter or meltingfurnace to the vacuum apparatus, I1 denotes the removable ladle in thevacuum chamber I, into which the metal is poured and in which thetreated metal is collected as the vacuum treatment is being carried out.Both the ladles I8 and II can be constructed identically, so thatexchanges can be made.

In the vacuum chamber I, there is a plurality of supports or piers I8,which are provided with sonically shaped attachments I! to serve asguides and supports tor the ladies and which cooperate with attachmentsZII on the ladles for that purpose. The ladies may be provided with aninsulating space between the outside plate shell and the lining of theladle. The ladles are also provided with stopper rods 22 for controllingthe flow of the liquid steel through the nozzles 23.

The vacuum chamber I is connected by means of a heavy duty pipe 21 andpipe-fitting assembly with any suitable air evacuating apparatus, for

instance, a steam-Jet air-ejector of such capacity as to quicklyevacuate the vacuum chamber and reduce the pressure in the vacuumchamber to a minimum low value, approximating zero.

The vacuum treatment is carried out in the following way: Liquid steelfrom a Bessemer converter, or melting furnace is tapped into the ladleI6, which is then taken to and supported above the vessel III. Theliquid steel is permitted to flow through the nozzle 23 of the ladle I6into the vessel III. The nozzle II in the bottom of the vessel III isopened, after the vessel III has been filled to a suitable height withliquid steel. From the vessel III, the steel is permitted to flow as astream 28 into the preheated ladle II in the vacuumchamber I.

The metal in the stream 28 will, during its passage through the vacuumchamber I, previously evacuated, become degasifled, and thedegasification continues afterwards with respect to the liquid mass ofsteel 29 which collects in the ladle I1.

In the vessel III may be added preheated or melted slag I5, as forinstance an acid reducing slag or any other suitable kind of slag, bywhich the liquid steel undergoing treatment may be acted on andpurified. Theslag I5 also protects the steel against oxidation andradiation of heat. The slag I5 is heated and melted to a substantiallyliquid state prior to being placed in the vessel I0, such preheating andmelting being accomplished by any suitable means forming no part of thepresent invention.

With the arrangement as shown, an electric heating oi! the steel may beeffected while passing through the vessel III. For this purpose thevessel III is designed as an open high frequency electric furnace. Alloi! the metal from the ladle I6 is cleansed while passing through thevessel II), by being brought into intimate contact with the slag I5under a circulating action created in the metal by the heating electriccurrent.

In the present instance, the capacity of the electric furnace I0 issubstantially one-tenth the capacity of the furnace or converter fromwhich the liquid metal is drawn into the ladle I8 Ior pouring into thevessel Ill.

After the pouring of the steel into the ladle II has been finished, andthe deoxidizing slag in the vessel Ill has also been drained or: intothe ladle II, the nozzle II is closed tightly by the stopper I2 topreserve the vacuum in the chamber I, to allow for further vacuumtreatment of the steel, and after degasiflcation and deoxidization oithe metal has been continued for the desired length of time, air isadmitted into the vacuum chamber, the lid 5 is removed and the ladle I1is hoisted out of the chamber I and taken to the place where the pouringof the steel into the moulds is to be done.

As it leaves the nozzle I I of the pouring box I I, through the suddenrelease of the gases as the metal enters the vacuum chamber I, thestream 2| oi liquid steel may assume the form or a spray, providingquicker and greater liberation of the occluded gases.

While the metal is held under the vacuum in the ladle I1, the minuteparticles oi the impurities coalesce and move upward to and collect atthe top of the static body of metal in th ladle II. By being able tohold the metal in a liquid state in the ladle I'I within the vacuumchamber I for a considerable length 01' time, the impurities are givenample opportunity to rise to the top.

The carrying out of the method as described above is, of course, to beconsidered as an example and the invention can be modified in differentways within the scope of the appended claims.

The process according to the invention can naturally be applied to thetreatment of metals other than steel. The apparatus shown admits of manyvarying possibilities for the treatment of liquid metals.

In addition to the dynamic and static vacuum treatment described above,the apparatus may be used for only static vacuum treatment, and theelectrical arrangements shown may be used simply for superheating themetal. Should, for instance, the metal in the ladle l'l, after thevacuum treatment, be too cold, the ladle I! may be hoisted and the emptyladle IE, or another similar ladle, placed in the vacuum chamber, and byagain pouring the metal through the vessel in the temperature of themetal may be raised to the desired degree by means of the electricheating arrangements.

I claim:

1. Method to deoxidize and degasiiy liquid steel, characterized by theliquid steel being tapped into a ladle from a Bessemer converter ormelting furnace, being then poured from said ladle through a smalleropen vessel into a ladle located in a vacuum chamber, wherein the metalduring its passagethrough said, vessel is electrically heated andbrought into intimate contact with a deoxidizing slag by action of theelectric heating currents, and wherein the metal during its passage fromsaid vessel to the ladle in the vacuum chamber is subjected to highvacuum to eifect degasifying of the metal.

2. Method to deoxidize and degasify liquid steel, characterized by theliquid steel being tapped into a ladle from a Bessemer converter ormelting furnace, being then poured from said ladle through a smalleropen vessel into a ladle located in a vacuum chamber, wherein the metalduring its passage through said vessel is electrically heated andbrought into intimate contact with a deoxidizing slag by action of theelectric heating currents, wherein the metal during its passage fromsaid vessel to the ladle in the vacuum chamber is subjected to highvacuum to effect degasifying of the metal, and wherein the vacuumtreatment is continued after the pouring of the metal into the ladle inthe vacuum chamber has stopped to continue said degasifying and topermit the impurities to rise to the top of the metal.

.3. An apparatus for the treatment of liquid steel, comprising a vacuumchamber, a ladle in said chamber, a ladle outside and above saidchamber, an open vessel between said ladles and in direct communicationwith the interior of said vacuum chamber, electric means for heating theliquid steel poured from the outside ladle through said pouring boxintothe ladle within the vacuum chamber, and means for drawing a high vacuumin said chamber to efiect said treatment of said liquid steel.

BALTZAR E. L. DE MARE.

